This invention relates to an improved micro lithographic writer that sweeps a modulated pattern across the surface of a workpiece. The SLM disclosed works in a diffractive mode with a continuous or quasi-continuous radiation source. It uses a long and narrow SLM and takes advantage of diffractive effects along the narrow axis of the SLM to improve writing characteristics along that axis.
Over time, optically-based systems for micro lithography have become increasingly sophisticated. Systems from more than a decade ago relied on swept laser beams, typically modulated using an acousto optical modulator. In the last decade, systems have been developed that use micro mirrors or deformable micro mirror devices to flash-stamp portions of the pattern, in so called maskless steppers. Under development are systems that use a narrow, one-dimensional micro-mirror array to sweep continuous or quasi-continuous laser energy across a substrate. Over the same period, the typical wavelength used for imaging has become shorter. The common characteristic of optically based systems has been a throughput advantage over competing e-beam systems.
Recent systems sweep radiation from a modulated one-dimensional micro-mirror array across the substrate. Advantages are high through-put, good utilization of the optical field, and the use of essentially-continuous lasers. An example is shown in FIG. 1 taken from application Ser. No. 12/718,895 by the same applicant. The figure shown depicts shows the SLM image as a square indicating a 2D SLM, but alternative forms with a 1D SLM can be found in the same application.
These systems using a 1D SLM provide good resolution and image characteristics across the long axis of the array, but provide much less favorable image characteristics in the direction of sweep, along the narrow axis of the array. Image characteristics along the length of the array benefit from use of diffraction effects between adjoining mirrors illuminated with partially coherent or locally coherent radiation. This is not an option along the direction of sweep, as interference depends on instantaneous interaction between radiation relayed from adjoining or adjacent the micro mirrors. Along the direction of sweep, adjacent pixels are printed at different times, so there is no interference.
Sigma™ tools, Micronic Laser's own flash and step systems based on a 2D SLM, are expensive and complex. Driving a million or more micro mirrors at ?? kHz frame rates requires an enormous amount of computation in a complex data path and the SLM device itself is complex.
One ancestor of Micronic Laser's Sigma™ tool is found in U.S. Pat. No. 5,523,193. In this patent, Nelson of Texas Instruments, describes an early generation of the deformable micro-mirror device. In column 7, the patent describes using an area array spatial light modulator in a flash-stamp and step mode similar to conventional mask-based stepper.
Another maskless lithography approach is found in U.S. Pat. No. 7,719,753. While the specification mentions many options in column 4, the principal teachings of the application from column 10 through column 16 involve use of a standard Texas Instruments deformable micro-mirror device. The preferred device, specified in column 16, is 1024 mirrors wide by 768 mirrors deep, corresponding to an early generation of HDTV. As the illumination source identified at the bottom of column 5 is an incoherent arc lamp. Accordingly, this patent teaches use of a new of device it is relatively difficult to keep loaded with data, that does not benefit from use of locally coherent or partially coherent illumination.
Also in the field of micro-lithography, but utilizing electron beams, is U.S. Pat. No. 6,870,172. This patent describes the so-called reflected electron beam lithography (REBL) system produced by KLA-Tencor Technologies. Like the preceding patent, it proposes use of a rectangular large array, with 4000×1000 individually addressed elements. It is an electron beam system, rather than an optical system.
As described above, modulated one-dimensional micro-mirror array systems have asymmetrical image characteristics. This complicates the patterning of substrates and is at odds with image characteristics of steppers. It would be useful to have a system that sweeps a one-dimensional micro-mirror SLM with essentially symmetrical image characteristics in and across the direction of sweep.
A better, more symmetrical system that sweeps a micro-mirror generated image across the substrate will be less complex and less expensive than flash-stamp and step systems. Additional applications can be devised for a more symmetrical system that cost-effectively uses fewer micro mirrors and relatively low-cost optical radiation sources.